Investigations of Hadron Structure using CB-TAPS at the Mainz Microtron

在 Mainz Microtron 使用 CB-TAPS 研究强子结构

• 批准号: SAPPJ-2018-00020
• 负责人: Hornidge, David
• 金额: $ 9.83万
• 依托单位: Mount Allison University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=653845
• 关键词: Investigations; Hadron; Structure; using; CB

The objective of this research proposal is to build upon our successful program of measuring polarization observables sensitive to the nucleon polarizabilities by continuing collaborative efforts with the A2 group at the Institute for Nuclear Physics in Mainz, Germany. We will exploit the 1.6-GeV MAMI-C continuous-wave electron beam to generate real photons, both polarized and unpolarized, which are combined with polarized and unpolarized nuclear targets in order to probe the structure of hadrons at intermediate energies. In this energy regime, description of structure and reaction dynamics lies in the transition region between nucleon/meson-based models and QCD-inspired models (or effective theories) based on quark/gluon degrees of freedom. Understanding hadronic structure in this transition region of non-perturbative QCD remains at the forefront of research efforts not only at the Mainz laboratory, but also at JLab in the USA, and other intermediate energy labs.******This project will focus specifically on topics within A2 that make use of the Crystal Ball and TAPS detectors. Over the last nine years in Mainz, Hornidge, Huber, and Sarty have been working on nucleon polarizability experiments in addition to studying threshold pion production. Sarty and Huber joined with Hornidge at MAMI in 2008, and this proposal is the third continuation of the Canadian contributions to the A2 Collaboration that will extend to the end of the decade. The experiments we are working on have not only high scientific impact, but they have very close scientific goals to the past, and planned, JLab projects of Huber and Sarty.******As part of our current project grant, we have taken data on four different Compton scattering polarization observables with the end goal of extracting both the scalar and spin polarizabilities of the proton with small statistical, systematic, and model-dependent errors. Such polarizabilities are fundamental structure quantities, amenable to calculation via various QCD-inspired models and effective theories. In addition to taking more data on three of these four asymmetries, over the next three years we will begin taking data on the neutron, where the polarizabilities are much less well known, and we intend to continue our feasibility studies of timelike virtual Compton scattering on the proton using dilepton production. This will allow us, for the first time, to access the timelike electromagnetic structure of the proton at low momentum transfer.******Finally, work will continue on the development and testing of an active, polarized target to use in both polarizability experiments and threshold pion production. By using such a target we will be able to improve on our double-polarization Compton measurements along with the target and beam-target asymmetry measurements in threshold pion production to test isospin breaking at the few percent level due to the up-down quark mass difference.

这项研究计划的目标是通过与德国美因茨核物理研究所的A2小组继续合作，在我们成功的测量对核子极化敏感的偏振观测数据的基础上，建立我们的计划。我们将利用1.6 gev的MAMI-C连续波电子束产生极化和非极化的实光子，并将其与极化和非极化核靶结合，以探测中能强子的结构。在这个能量体系中，结构和反应动力学的描述位于基于核子/介子的模型和基于夸克/胶子自由度的qcd启发模型（或有效理论）之间的过渡区域。了解非微扰QCD过渡区的强子结构，不仅在美因茨实验室，而且在美国JLab和其他中间能量实验室都是研究工作的前沿。******该项目将特别关注A2中使用水晶球和TAPS探测器的主题。在过去的九年里，在美因茨，Hornidge， Huber和Sarty除了研究阈值介子的产生外，还一直在进行核子极化实验。Sarty和Huber与Hornidge于2008年加入了MAMI，该提案是加拿大对A2协作的第三次延续，将延续到本十年末。我们正在进行的实验不仅具有很高的科学影响，而且它们的科学目标与Huber和Sarty过去和计划中的JLab项目非常接近。******作为我们当前项目拨款的一部分，我们收集了四个不同的康普顿散射极化观测数据，最终目标是在统计、系统和模型相关的小误差下提取质子的标量和自旋极化。这种极化率是基本的结构量，可以通过各种qcd启发的模型和有效的理论来计算。除了对这四种不对称中的三种进行更多的数据采集之外，在接下来的三年里，我们将开始对中子进行数据采集，因为中子的极化率鲜为人知，我们打算继续利用双轻子产生对质子进行类时虚拟康普顿散射的可行性研究。这将使我们第一次，接触到质子在低动量转移时的类时电磁结构。******最后，工作将继续开发和测试一个有源，偏振目标，用于极化实验和阈值介子生产。通过使用这样一个目标，我们将能够改进双偏振康普顿测量以及靶和束靶不对称测量在阈值介子产生中，以测试由于上下夸克质量差导致的同位旋破断在几个百分点的水平。